1. Field of the Invention
The present invention relates to a camera using a recording medium which electronically develops an image obtained by exposing the recording medium, and more particularly, to a device controlling a photographing operation of the camera.
2. Description of the Related Art
Conventionally, there is known a photographic material which electronically develops an optical image formed thereon through a photographing lens. Japanese Unexamined Patent Publication No. 5-2280, for example, discloses a recording material which is a combination of an electrostatic information recording material and an electric charge keeping medium. In this specification, such a recording medium is referred to as an electro-developing recording material, and a camera using the electro-developing recording material is referred to as an electro-developing type camera.
In the electro-developing recording medium disclosed in the above publication, the electrostatic information recording material has a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium has a liquid crystal display. In this structure, when the electrostatic information recording material is exposed while an electric voltage is applied to the electrostatic information recording material and the electric charge keeping medium, an electric charge in accordance with the amount of incident light is generated in the electrostatic information recording material. Since the intensity of an electric field applied to the liquid crystal display facing the electrostatic information recording material varies in accordance with the generated electric charge, an image corresponding to the amount of light distribution is indicated or developed on the liquid crystal display.
Japanese Unexamined Patent Publication Nos. 5-150251, 5-165005, 6-130347 and 7-13132 disclose a liquid crystal display in which an image indicated on the liquid crystal display is kept even if the electric field applied to the liquid crystal display is removed.
The contrast of the image indicated on the liquid crystal display becomes greater in proportion with the time an electric voltage is started to be applied to the electro-developing recording medium, and when the image is bright, the contrast reaches a maximum when the electric voltage has been applied to the electro-developing recording medium for a predetermined period. Therefore, by stopping the voltage application at that time, an image having a high contrast can be obtained. Conversely, in order for the contrast to reach a maximum when the image is dark, the electric voltage needs to be applied to the electro-developing recording medium for a period longer than the predetermined period, therefore the contrast does not become great enough even if the voltage applying time is long. Thus, in this instance, the voltage applying time onto the electro-developing recording medium is set so that a contrast having a predetermined degree is obtained rather than for a predetermined time.
Nevertheless, when the exposure period for which the electro-developing recording medium is exposed is longer than the voltage applying time which is obtained by an exposure calculation based on a photometry value, a problem occurs in which a clear image cannot be recorded on the electro-developing recording medium, since the voltage applying is stopped during the exposure. On the other hand, as disclosed in Japanese Unexamined Patent Publication No. 3-278342, by setting an electric voltage, which is applied to the electro-developing recording medium, to a low value, the voltage applying time can be prolonged, but a problem occurs in that the liquid crystal display cannot display a clear image if the applied voltage is too low.